netdev - Re: [PATCH v2 net-next] tcp: set SOCK

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Message-ID: <1431701423.27831.101.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 15 May 2015 07:50:23 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Baron <jbaron@...mai.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next] tcp: set SOCK_NOSPACE under memory pressure

On Fri, 2015-05-15 at 10:20 -0400, Jason Baron wrote:
> On 05/14/2015 11:07 PM, Eric Dumazet wrote:
> > On Sat, 2015-05-09 at 17:38 -0400, David Miller wrote:
> >> Applied, thanks a lot for adding so much information to the commit
> >> message.
> >> --
> > When doing more tests with this stuff, I found we could still have
> > hangs, because a TCP socket can end up having no skb in its write queue.
> >
> > We need to allow one skb (this can be 2KB) to keep the logic being ACK
> > driven.
> >
> 
> Indeed. I alluded to that in the commit message.
> 
> The 2KB minimum wouldn't help in the case where we really got
> -ENOMEM from the core allocator, unless I guess we reserved
> the 2KB permanently. Or we could just issue the wakeup in the
> case where we return -EAGAIN and the write queue is empty.
> That is a very simple additional change here, I think.

I cooked a patch series, will send it very soon.

The ENOMEM in core allocator is very unlikely, as we use GFP_KERNEL.

Normally, memcg and/or tcp_mem[] should prevent this from happening.



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